Hydrocarbon alkylation is widely used in the petroleum refining industry. It is used to make a variety of useful acyclic hydrocarbon products. These products are consumed in motor fuel and as petrochemical feedstocks.
Alkylation comprises reacting two feedstocks, an alkylation substrate and an alkylation agent. To produce motor fuels, the alkylation substrate is an isoparaffin, commonly isobutane, and the alkylation agent is an olefin, usually propylene or butenes. Large amounts of paraffins for high-octane gasoline are made by alkylating isobutane with propylene or butenes in large-scale commercial facilities. Liquid phase hydrofluoric acid (HF) or sulfuric acid is often used as the catalyst. Because liquid acids are volatile and the environmental risks arising from an accidental release to the atmosphere are more and more undesirable, solid catalysts have been proposed for alkylation to produce motor fuels.
Isomerization of normal paraffins is widely used in the petroleum refining industry. Butane isomerization is integrated with alkylation in multi-step processes to increase butane utilization. The normal butanes are isomerized and the resultant isobutane is consumed in the alkylation reaction with olefins. Such processes are described in U.S. Pat. No. 4,324,937 and in Chapter 9.2 of the book titled Handbook of Petroleum Refining Processes, edited by Robert A. Meyers, Second Edition, McGraw-Hill, New York, 1997, ISBN 0-07-041796-2 (hereinafter, Handbook). The debutanizer distillation column of the integrated process is commonly called an isostripper since it produces an overhead for recovering isobutane and a side draw for separately recovering normal butane. (In contrast, where the debutanizer distillation zone has no separate side draw for normal butane and instead recovers isobutane and normal butane together in one or more overhead streams, then the debutanizer distillation zone is commonly called a debutanizer.) The side draw has a suitably high normal butane content so that it can be combined with makeup hydrogen, heated, and charged to the isomerization reactor. The isomerization reaction zone effluent is cooled and passes to a distillation column commonly called a stabilizer. The stabilizer overhead is a light gas byproduct. The stabilizer bottoms stream contains isobutane and passes to the isostripper, where any isobutane is recovered in the isostripper overhead and flows to the alkylation reactor. Any unconverted normal butane is recovered in the isostripper's side draw for return to the isomerization reactor. Any heavier hydrocarbons in the stabilizer bottoms stream are recovered in the isostripper bottoms stream.
Economical and efficient ways are sought to improve the integration of alkylation and isomerization processes.